Noise-canceling earphones are used to provide desired sound signals to a listener while reducing unwanted external noises. Passive noise reduction techniques physically prevent sound waves from reaching a listener's ear by using insulation or dampening (e.g., an earcup that surrounds or rests on the ear) to reduce undesired sounds from interfering with a desired sound signal. However, these techniques are best at reducing middle and high frequencies. To further reduce unwanted external noises, some earphones use active noise cancellation techniques, a process for reducing unwanted sound through destructive interference, by adding an additional out-of-phase sound designed to cancel the unwanted sound.